Deck 9: Conjugation and Aromaticity

Question 1

How many atoms are part of the conjugated system of the molecule shown below?

A)5
B)8
C)11
D)12

Answer 1

12

Question 2

Which of the following is considered non-aromatic?

A)
B)
C)
D)

Answer 2

Question 3

Which of the following does NOT represent a conjugated system?

A)
B)
C)
D)

Answer 3

Question 4

What is the configuration around the centre sigma bond of butadiene shown below?

A)cis
B)trans
C)s-cis
D)s-trans

Question 5

Which resonance form of anthracene contributes more towards it's stability?

A)A because it's more aromatic
B)A because it's less aromatic
C)B because it's more aromatic
D)B because it's less aromatic

Question 6

Which of the following best represents the HOMO of butadiene shown below?

A)
B)
C)
D)

Question 7

Which of the following best represents the HOMO of the pentadienyl anion shown below?

A)
B)
C)
D)

Question 8

Which of the following best represents the LUMO of hexatriene shown below?

A)
B)
C)
D)

Question 9

How many nitrogen lone pairs are involved in the aromaticity of the following molecule?

A)0
B)1
C)2
D)3

Question 10

How many atoms are part of the conjugated system of the molecule shown below?

A)6
B)7
C)11
D)13

Question 11

Which of the following compounds is considered non-aromatic?

A)
B)
C)
D)

Question 12

Which of the following is NOT a criterion for aromaticity?

A)be cyclic and planar
B)have a p-orbital on all participating ring atoms
C)have 4n+2 number of delocalized ð electrons
D)have an even number of atoms involved in the aromatic system

Question 13

Which of the following best describes the bond length of the central sigma bond in 1,3-butadiene shown below?

A)It is longer than an average C-C sigma bond.
B)It is shorter than an average C-C sigma bond.
C)It is the same length as an average C-C sigma bond.
D)There is not enough information to determine bond length.

Question 14

Which of the following best describes the molecule shown below?

A)aromatic
B)non-aromatic
C)anti-aromatic
D)symmetrical

Question 15

Why does an increase in conjugation lead to an increase in absorption wavelength?

A)Increased conjugation leads to a smaller gap in energy between the HOMO and LUMO.
B)Increased conjugation leads to a larger gap in energy between the HOMO and LUMO.
C)Increased conjugation leads to a smaller gap in energy between the ó and ó* orbitals.
D)Increased conjugation leads to a larger gap in energy between the ó and ó* orbitals.

Question 16

Which molecule would be expected to have the higher absorption wavelength?

A)A because it's more conjugated
B)A because it's less conjugated
C)B because it's more conjugated
D)B because it's less conjugated

Question 17

Compared to ethene,butadiene would be expected to absorb light with which of the following properties?

A)higher wavelength and higher energy
B)higher wavelength and lower energy
C)lower wavelength and higher energy
D)lower wavelength and lower energy

Question 18

Which of the following ions is considered anti-aromatic?

A)
B)
C)
D)

Question 19

Which of the following best represents the LUMO of the propenyl cation shown below?

A)
B)
C)
D)

Question 20

How many atoms are part of the conjugated system of (+)- Frondonsin B shown below?

A)5
B)8
C)10
D)12

Question 21

What is the hybridization of the nitrogen atom in the structure shown below?

A)s
B)p
C)sp²
D)sp³

Question 22

What is the hybridization of the oxygen atom in furan?

A)sp
B)sp²
C)sp³
D)p

Question 23

Which of the following best describes the following molecule?

A)aromatic
B)anti-aromatic
C)non-aromatic
D)somewhat aromatic

Question 24

Conjugated systems are more stable than non-conjugated systems.

Question 25

Which of the following best describes double bonds in aromatic systems?

A)They are more susceptible to hydrogenation than non-aromatic double bonds.
B)They are less susceptible to hydrogenation than double bonds.
C)They are equally susceptible to hydrogenation when compared to non-aromatic double bonds.
D)There is no difference between an aromatic and non-aromatic double bond.

Question 26

How many nodal planes does the following representation of benzene have?

A)0
B)1
C)2
D)3

Question 27

How many nodal planes does the following representation of benzene have?

A)1
B)2
C)3
D)6

Question 28

Which of the following compounds would liberate the most heat when hydrogenated and why?

A)A because it's conjugated.
B)A because it's not conjugated.
C)B because it's conjugated.
D)B because it's not conjugated.

Question 29

How many nodal planes does the following representation of benzene have?

A)0
B)1
C)2
D)3

Question 30

Which of the following is an accurate description of benzene?

A)There are two distinct structures in equilibrium.
B)All the carbon-carbon bonds are the same length.
C)Some carbon-carbon bonds are longer than others.
D)There are distinct single and double bonds.

Question 31

s-cis is a more stable confirmation then s-trans.

Question 32

Which of the following statements best describes the molecule below,assuming planarity?

A)It contains 6 ð electrons and is aromatic.
B)It contains 8 ð electrons and is non-aromatic.
C)It contains 8 ð electrons and is aromatic.
D)It contains 8 ð electrons and is anti-aromatic.

Question 33

How many ð electron pairs are in the following molecule of benzamide?

A)3
B)4
C)5
D)6

Question 34

Increased conjugation leads to an increase in absorption wavelength.

Question 35

In the aromatic compound resonance form shown below,which heteroatoms are contributing lone pairs towards aromaticity?

A)nitrogen only
B)oxygen only
C)both nitrogen and oxygen
D)neither nitrogen or oxygen

Question 36

How many electrons pairs are part of the conjugated system in the molecule shown below?

A)0
B)2
C)3
D)4

Question 37

Which of the following best describes anti-aromatic compounds?

A)They are not planar.
B)They are not cyclic.
C)They don't have p orbitals on all participating ring atoms.
D)They don't follow the 4n+2 rule.

Question 38

How many ð electron pairs are present in the following aromatic heterocycle?

A)2
B)3
C)4
D)5

Question 39

Which of the following best describes the cyclopentadienyl radical shown below?

A)aromatic
B)anti-aromatic
C)non-aromatic
D)somewhat aromatic

Question 40

The bond length of a conjugated double bond is the same length as a non-conjugated double bond.

Question 41

The nitrogen atom in amide bonds is sp³ hybridized.

Question 42

Assuming planarity,the following ion is considered aromatic.

Question 43

Lone pairs cannot be a part of conjugated systems.

Question 44

Alkynes cannot be a part of conjugated systems.

Question 45

Sigma bonds in conjugated systems have a larger energy barrier to rotation then sigma bonds in non-conjugated systems.

Question 46

The larger the difference in energy between the HOMO and LUMO,the larger the wavelength of light a molecule will absorb.

Question 47

Anti-aromatic compounds can be non-planar.

Question 48

Given the option,molecular structures tend to exist as non-aromatic instead of anti-aromatic.

Question 49

Energy of light is inversely proportional to its wavelength.

Question 50

Any molecule that follows Hückel's rule is aromatic.

Question 51

Assuming planarity,the following ion is considered anti-aromatic.

Question 52

All lone pair electrons are considered ð electrons.

Question 53

All planar molecules are considered aromatic.

Question 54

A molecule must be planar to be considered aromatic.

Question 55

Carbanions are anti-aromatic,whereas carbocations are aromatic.

Question 56

Assuming planarity,the following molecule is considered aromatic.

Question 57

Amide bonds undergo free rotation at room temperature.

Question 58

Only ð electrons contribute towards aromaticity.

Question 59

Anti-aromatic compounds are also considered non-aromatic.

Question 60

Assuming planarity,the following molecule is considered non-aromatic.

Question 61

Benzene has a _______________ heat of hydrogenation compared to the corresponding 1,3,5-hexatriene.

Question 62

A molecule that is anti-aromatic has _______________ electrons in its conjugated ring system.

Question 63

Aromatic double bonds tend to be _______________ stable than their corresponding non-aromatic double bonds.

Question 64

Both pyridine and pyrrole shown below have a lone pair of electrons on their nitrogen capable of acting as a base.Which compound would you expect to be the stronger base.Why?

Question 65

The hybridization of a nitrogen atom in an amide bond is _______________ hybridized.

Question 66

LUMO is an acronym for the _______________ .

Question 67

_______________ circles are a method of mapping out aromatic orbital diagrams.

Question 68

Indicate which atoms are part of the conjugated system shown below

Question 69

The following molecule shown below is Lipitor,a drug prescribed to lower cholesterol levels.How many aromatic rings does it contain,how many ð electron pairs are part of its conjugated system,and how many atoms are part of its conjugated system?

Question 70

A molecule that is aromatic has _______________ electrons in its conjugated ring system.

Question 71

Draw two other resonance states of naphthalene showing electron flow.Predict whether you expect the bond between C1-C2 or C2-C3 to be longer in the figure shown below.

Question 72

Benzyne (shown below)is a highly reactive yet still aromatic derivative of benzene.It is planar and cyclic,but has eight ð electrons instead of six.Explain how it is still aromatic yet but still defies Hückel's rule.

Question 73

Demonstrate why in compound A,the nitrogen is more likely to act as a base,whereas in compound B,the oxygen atom is more likely to act as a base.Use resonance structures to justify your answers.

Question 74

Conjugated systems tend to add rigidity to molecules.

Question 75

Which molecule shown below would you expect to have the larger dipole moment.Draw resonance structures using electron flow arrows for both molecules to show why.

Question 76

HOMO is an acronym for the _______________ .

Question 77

Show electron flow and draw a resonance state to show why the following molecule is aromatic.

Question 78

A molecule that follows all criteria for aromaticity except only contains 4n delocalized electrons in the ring is said to be _______________.

Question 79

Two molecular orbitals that lie in the same energy are said to be _______________ .

Question 80

Indicate which bonds are rotatable in the heterocyclic molecule Kibdelone C shown below,ignoring methyl groups.